This application concerns a method of controlling a three-level power inverter using a two-level power inverter controller, and an apparatus for implementing the same.
It is known that when creating a power inverter/inverter controller scheme a three-level inverter has many advantages over a two-level inverter. Among these advantages are an increased power rating, improved harmonic performance, and a reduction in the electromagnetic interference. A “two-level” inverter (converter) utilizes a control signal comprising two digital signals; one drives the top power switch while the other drives the bottom switch. The combination of these digital signals into a single control signal results in a signal having two steps, i.e. one (logic 1) representing the time to turn-on a positive voltage and zero (logic 0) representing the time to turn-on a negative voltage. During the transition time the control wave is positioned as a transition edge between up and down. In real applications, there is always a need of a short time interval called “dead-time” where neither top or bottom power switch will be turned-on. This short time interval is inherently needed to be inserted as a mean to prevent the shoot-through condition and would not be discussed in details herein. A “three-level” inverter, on the other hand, utilizes a control signal comprising three digital signals. This results in an output voltage comprised of three voltage levels for each single phase: a positive voltage, a zero voltage and a negative voltage. Since a three-level inverter requires the input of a control wave having three steps, and a two-level inverter controller can only output a control wave having two steps, some processing should be done on the control signal from the two-level inverter controller to make it compatible with a three-level inverter.
It is also known that many current applications and devices utilize a two-level inverter controller. Should a user wish to connect a three-level inverter to any of these devices, a converter should be used for the reasons described above. While two-level inverters are known in the art, all currently known two-level inverters introduce unacceptably high levels of harmonics and electrical noise into the system resulting in poor power quality, as well as other potential drawbacks.